Method of transmitting and receiving frame for uplink multi-user multiple-input and multiple-output (UL MU-MIMO) communication

ABSTRACT

Provided is a method of transmitting and receiving a frame for a multi-user multiple-input and multiple-output (MU-MIMO) communication in an access point (AP), the method including determining at least one transmission station (STA), transmitting, to the transmission STA, an uplink multi-user poll (UL MU poll) frame requesting a data frame, receiving the data frame from the at least one transmission STA simultaneously, and transmitting an acknowledgement (ACK) frame to the at least one transmission STA in response to the receiving.

CROSS-REFERENCE TO RELATED APPLICATION

This application a continuation of and claims priority to U.S.application Ser. No. 16/277,961, filed Feb. 15, 2019, which is acontinuation of and claims priority to U.S. application Ser. No.15/649,887, filed Jul. 14, 2017, now U.S. Pat. No. 10,250,304, which isa continuation of and claims priority to U.S. application Ser. No.14/453,419 filed Aug. 6, 2014, now U.S. Pat. No. 9,838,093, which claimsthe priority benefit of Korean Patent Application No. 10-2013-0093199,filed on Aug. 6, 2013, Korean Patent Application No. 10-2013-0112733filed on Sep. 23, 2013, and Korean Patent Application No.10-2014-0014068 filed on Feb. 7, 2014 in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein byreference.

BACKGROUND 1. Field of the Invention

Embodiments of the present invention relate to a media access control(MAC) protocol of a wireless local area network (WLAN), and moreparticularly, to a configuration of a frame for use in frametransmission based on uplink multi-user multiple-input andmultiple-output (MU-MIMO) technology.

2. Description of the Related Art

Recently, in wireless communication systems, a multiple-input andmultiple-output (MIMO) technology for transmitting and receiving datausing at least two antennas is being generalized. A wireless local areanetwork (WLAN) also enables at least two transmission antennas to beused from the Institute of Electrical and Electronics Engineers (IEEE)802.11n standard. The IEEE 802.11n standard allows for use of up to fourantennas, and the IEEE 802.11ac standard allows for use of up to eightantennas. For example, in a case of using a great number of transmissionantennas, data transmission may be performed based on transmitbeamforming technology, thereby improving a performance of signalreception.

For efficient use of frequency resources, the IEEE 802.11ac for whichstandardization is in progress may include downlink multi-usermultiple-input and multiple-output (MU-MIMO) technology enabling anaccess point (AP) to simultaneously transmit beamformed data frames to aplurality of stations (STAs). Also, research is being conducted intouplink (UL) MU-MIMO technology enabling transmission of data frames tothe AP from the plurality of STAs and reception of the data frames atthe AP through being separated for each stream, to be conductedsimultaneously.

FIG. 1A illustrates an example of an operation in which at least twoSTAs transmit data to an AP according to a related art. An STA 1 and anSTA 2 may initiate a random backoff when a channel is in an idle state.In FIG. 1A, the STA 1 terminating the random backoff earlier than theSTA 2 may transmit a data frame 1 to the AP, and receive a firstacknowledge (ACK) frame. Since the STA 2 listens to frames transmittedby the STA 1, the STA 2 may standby in a state of suspending the randombackoff. When the ACK frame ends, the STA 2 may continue the randombackoff, and transmit a data frame 2 to the AP.

FIG. 1B illustrates an example of an operation in which at least twoSTAs transmit data to an AP based on UL MU-MIMO technology according toa related art.

Similar to the operation of FIG. 1A, an STA 1 and an STA 2 may initiatea random backoff when a channel is in an idle state. The STA 1terminating the random backoff earlier than the STA 2 may transmit, tothe AP, a data frame 1 on which beamforming is performed. Due to thebeamforming, the STA 2 may not listen to the data frame 1. Thus, the STA2 may process the random backoff without suspending transmission, andtransmit a data frame 2 on which beamforming is performed to the AP.

When the data frame 2 is received during reception of the data frame 1,a physical (PHY) layer of the AP may abnormally perform data reception.Based on a known research result, UL MU-MIMO frames may need to betemporally synchronized within an error range of less than 100nanoseconds (ns) to receive data.

Accordingly, UP MU-MIMO data reception may not be performed using anexisting method.

SUMMARY

According to an aspect of the present invention, there is provided amethod of transmitting and receiving a frame for a multi-usermultiple-input and multiple-output (MU-MIMO) communication in an accesspoint (AP), the method including determining at least one transmissionstation (STA), transmitting, to the transmission STA, an uplinkmulti-user poll (UL MU poll) frame requesting a data frame, receivingthe data frame from the at least one transmission STA simultaneously,and transmitting an acknowledgement (ACK) frame to the at least onetransmission STA in response to the receiving.

The UL MU poll frame may include identification information on the atleast one transmission STA.

The identification information may include at least one of media accesscontrol (MAC) address information, association identification (AID)information, and partial AID information in an Institute of Electricaland Electronics Engineers (IEEE) 802.11ac.

The UL MU poll frame may include at least one of information on atransmission time and information on a number of transmission STAs.

The transmitting of the UL MU poll frame may include transmitting basedon MU-MIMO technology or transmitting in an unbeamformed state.

The receiving may include receiving the data frame based on MU-MIMOtechnology.

The transmitting of the ACK frame may include transmitting a group ACKframe including at least one of identification information on the atleast one transmission STA and a bitmap obtained by mapping the at leastone transmission STA to a single bit.

The transmitting of the ACK frame may include transmitting the group ACKin an unbeamformed state.

The transmitting of the ACK frame may include transmitting at least oneACK frame including identification information on the at least onetransmission STA.

The transmitting of the ACK frame may include transmitting the at leastone ACK frame based on MU-MIMO technology.

According to another aspect of the present invention, there is alsoprovided a method of transmitting and receiving a frame for an MU-MIMOcommunication in a transmission STA, the method including receiving,from an AP, a UL MU poll frame requesting a data frame, transmitting thedata frame to the AP after a predetermined period of time elapses from atime at which the UL MU poll frame is received, and receiving an ACKframe responding to receiving of the data frame.

The UL MU poll frame may include identification information on thetransmission STA.

The identification information may include at least one of MAC addressinformation, AID information, and partial AID information in an IEEE802.11ac.

The UL MU poll frame may include at least one of information on atransmission time and information on a number of transmission STAs.

The receiving of the UL MU poll frame may include receiving based onMU-MIMO technology or receiving in an unbeamformed state.

The transmitting of the data frame may include transmitting the dataframe based on the MU-MIMO technology.

The receiving of the ACK frame may include receiving a group ACK frameincluding at least one of a bitmap obtained by mapping the transmissionSTA to a single bit and identification information on the transmissionSTA.

The receiving of the ACK frame may include receiving the group ACK framein an unbeamformed state.

The receiving of the ACK frame may include receiving the ACK frameincluding the identification information on the transmission STA.

The receiving of the ACK frame may include receiving the ACK frame basedon the MU-MIMO technology.

According to still another aspect of the present invention, there isalso provided an AP for use in an MU-MIMO communication, the APincluding a controller to determine at least one transmission STA, and acommunicator to transmit a UL MU poll frame to the at least onetransmission STA, receive a data frame from the at least onetransmission STA simultaneously, and transmit an ACK frame to the atleast one transmission STA in response to receiving of the data frame.

According to yet another aspect of the present invention, there is alsoprovided a transmission STA for use in an MU-MIMO communication, the STAincluding a communicator to receive, from an AP, a UL MU poll framerequesting a data frame, and a controller to control the communicator totransmit the data frame to the AP after a predetermined period of timeelapses from a time at which the UL MU poll frame is received, whereinthe communicator receives an ACK frame responding to receiving of thedata frame.

The communicator may transmit the data frame based on MU-MIMOtechnology, receive a group ACK frame in an unbeamformed state, andreceive the ACK frame including identification information on thetransmission STA based on the MU-MIMO technology.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features, and advantages of the inventionwill become apparent and more readily appreciated from the followingdescription of exemplary embodiments, taken in conjunction with theaccompanying drawings of which:

FIGS. 1A and 1B are diagrams illustrating examples of an operation inwhich at least two stations (STAs) transmit data to an access point (AP)according to a related art;

FIG. 2 is a block diagram illustrating an AP and STAs according to anexample embodiment;

FIG. 3 is a timing diagram illustrating an example of operating an APand an STA according to an example embodiment;

FIG. 4 is a diagram illustrating a configuration of an uplink multi-userpoll (UL MU poll) frame according to an example embodiment;

FIG. 5 is a diagram illustrating an example of a group acknowledgement(ACK) frame according to an example embodiment;

FIG. 6 is a diagram illustrating another example of a group ACK frameaccording to an example embodiment;

FIG. 7 is a diagram illustrating an example of an uplink multi-usermultiple-input and multiple-output (MU-MIMO) data transmission protocolaccording to an example embodiment; and

FIG. 8 is a diagram illustrating another example of a UL MU-MIMO datatransmission protocol according to an example embodiment.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments will be described in detail withreference to the accompanying drawings. However, it should be understoodthat these embodiments are not construed as limited thereto. Likereference numerals in the drawings denote like elements.

The terms used in this specification were selected to include current,widely-used, general terms, in consideration of the functions of thepresent invention. However, the terms may represent different meaningsaccording to the intentions of the skilled person in the art oraccording to customary usage, the appearance of new technology, etc.

In certain cases, a term may be one that was arbitrarily established bythe applicant. In such cases, the meaning of the term will be defined inthe relevant portion of the detailed description. As such, the termsused in the specification are not to be defined simply by the name ofthe terms but are to be defined based on the meanings of the terms aswell as the overall description of the present invention.

FIG. 2 is a block diagram illustrating an access point (AP) 100 andstations (STAs) 200-1 through 200-n according to an example embodiment.

Referring to FIG. 2, the AP 100 may include a controller 110 and acommunicator 120.

The controller 110 may generate a frame transmitted by the communicator120. The controller 110 may process a frame received by the communicator120. The controller 110 may control the communicator 120 to communicatewith at least one of communicators 220-1 through 220-n of the STAs 200-1through 200-n based on a multiple-input and multiple-output (MIMO)scheme.

The controllers 210-1 through 210-n may process frames received by thecommunicators 220-1 to 220-n, or generate frames transmitted by thecommunicators 220-1 through 220-n. The controllers 210-1 through 210-nmay control the communicators 220-1 through 220-n to transmit a dataframe after a short interframe space (SIFS) from a time at which anuplink multi-user poll (UL MU poll) frame is received.

The controller 110 or each of the controllers 210-1 through 210-n may beimplemented by, for example, an integrated circuit (IC) chip, amicroprocessor, a minicomputer, and the like. The controller 110 or eachof the controllers 210-1 through 210-n may determine, for example, anSTA communicating with the communicator 120. The controller 110 or eachof the controllers 210-1 through 210-n will be further explained withreference to the following descriptions.

The communicator 120 of the AP 100 may communicate with at least one ofthe communicators 220-1 through 220-n of the STAs 200-1 through 200-n.The communicator 120 of the AP 100 may transmit or receive the UL MUpoll frame, the data frame, and an acknowledgement (ACK) frame to orfrom at least one of the communicators 220-1 through 220-n of the STAs200-1 through 200-n. The communicator 120 may include a communicationmodule such as an antenna, a modulator/demodulator, a frequencyprocessing device, a filtering device, and the like.

FIG. 3 is a timing diagram illustrating an example of operating an AP100 and an STA 200 according to an example embodiment.

In operation 310, the AP 100 may determine a transmission STA totransmit a data frame. For example, the AP 100 may determine at leastone of a plurality of STAs, for example, the STAs 200-1 through 200-n ofFIG. 2, to be the transmission STA.

In operation 320, the AP 100 may transmit a UL MU poll frame to the STA200. The UL MU poll frame may be a frame identifying a transmission STAand a frame instructing the transmission STA to transmit the data frame.The transmission STA may be preset to transmit the data frame after apredetermined period of time, for example, an SIFS, elapses in responseto receiving the UL MU poll frame. As another example, the AP 100 mayperform a request to send/clear to send (RTS/CTS) exchange beforetransmitting the UL MU request frame.

A configuration of the UL MU poll frame according to an exampleembodiment may be indicated with reference to FIG. 4. Referring to FIG.4, the UL MU poll frame may include a frame control field, a receiveraddress (RA) field, a transmitter address (TA) field, a UL MU-MIMOcommon information (UL MU-MIMO info) field, transmission STA information(STA info) fields, and a frame check sequence (FCS) field. As describedabove, the UL MU poll frame may include the transmission STA fields, andinclude identification information on transmission STAs corresponding toSTA1 through STAn. In an embodiment, the identification information oneach of the transmission STAs may include at least one of media accesscontrol (MAC) address information, association identification (AID)information, and partial AID information in the Institute of Electricaland Electronics Engineers (IEEE) 802.11ac.

The UL MU poll frame may include UL MU-MIMO common information. The ULMU-MIMO common information may include a value of a transmission timeinformation field, for example, an L-LENGTH, included in an L-SIG of aphysical (PHY) layer overhead, and a number of STAs to simultaneouslytransmit data frames. Here, “being simultaneous” may be used to indicatea degree of identicalness in terms of a time, or being provided within apredetermined error range. The L-LENGTH may be used for a LENGTH valueincluded in an L-SIG of a beamformed data frame to be transmitted byeach of the STAs during a UL MU-MIMO transmission interval. In thepresent disclosure, a transmission time may refer to a period of timeduring which transmission is performed.

When a PHY protocol data unit (PPDU) type of the beamformed data frameis a high throughput (HT) PPDU or a very high throughput (VHT) PPDU, aLENGTH field of the L-SIG may be changed to a temporal length of aframe. Thus, when each of the STAs transmits the data frame, data ofwhich an amount corresponds to the temporal length indicated in theL-LENGTH may be transmitted.

Referring back to FIG. 3, the STA 200 may receive a UL MU poll frame.The STA 200 may determine whether the STA 200 is the transmission STA byverifying identification information on the transmission STA in the ULMU poll frame.

In operation 330, when the STA 200 is the transmission STA, the STA 200may transmit the data frame after the SIFS in response to receiving theUL MU poll frame. Other STAs may also receive UL MU poll frames andtransmit data frames after the SIFS. Thus, all transmission STAs maysimultaneously transmit data frames to the AP.

In operation 340, the AP 100 may transmit an ACK frame to the STA 200corresponding to the transmission STA. The AP 100 may need to transmitthe ACK frame to all transmission STAs. To this end, the AP 100 may usea group address indicating a predetermined UL MU-MIMO group to be areceiver address (RA). An ACK frame including the group address may bereferred to as a group ACK frame.

FIG. 5 is a diagram illustrating an example of a group ACK frameaccording to an example embodiment, and FIG. 6 is a diagram illustratinganother example of the group ACK frame according to an exampleembodiment. Referring to FIG. 5, a group address, for example, a UL MUgroup, may be included in an RA field. In an embodiment, the groupaddress may include identification information on a transmission STAsuccessfully receiving a data frame, to provide notification on whetherthe data frame is received.

Referring to FIG. 6, a UL MU ACK bitmap may be included in a group ACKframe. The UL MU ACK bitmap may be a bitmap obtained by mapping a singlebit to a single STA. The UL MU ACK bitmap may be formed based on asequential order and a list of STAs included in a UL MU poll frame as areference.

In an embodiment, at least one of the UL MU poll frame and the ACK framemay be transmitted based on a downlink MU-MIMO technology, ortransmitted in an unbeamformed state.

FIG. 7 is a diagram illustrating an example of a UL MU-MIMO datatransmission protocol according to an example embodiment, and FIG. 8 isa diagram illustrating another example of the UL MU-MIMO datatransmission protocol according to an example embodiment. For example, adata transmission protocol used when MU-MIMO technology is not appliedto a UL MU poll frame and a group ACK frame may be indicated withreference to FIG. 7.

Referring to FIG. 7, for protection, an AP may perform an RTS/CTSexchange before transmitting a UL MU poll frame. For example, the AP mayperform a backoff after a channel busy interval. When the backoff isperformed, the AP may transmit RTS frames to STAs including an STA 1 andan STA 2. In response to receiving the RTS frames, the STAs may transmitCTS frames to the AP after an SIFS.

When the CTS frames are received, the AP may transmit the UL MU pollframe to transmission STAs including the STA 1 and the STA 2 after theSIFS. The UL MU poll frame may be transmitted in an unbeamformed state.

The transmission STAs may transmit data frames including a data frame 1and a data frame 1 after the SIFS in response to receiving the UL MUpoll frame. The data frames may be transmitted based on MU-MIMOtechnology.

The AP may receive the data frames, and then transmit a group ACK frameto each of the transmission STAs after the SIFS. The group ACK frame maybe transmitted in an unbeamformed state.

A data transmission protocol used when a UL MU poll frame and a groupACK frame are transmitted based on downlink MU-MIMO technology may beindicated with reference to FIG. 8.

Referring to FIG. 8, for protection, an AP may perform an RTS/CTSexchange before transmitting a UL MU poll frame. For example, the AP mayperform a backoff after a channel busy interval. When the backoff isperformed, the AP may transmit RTS frames to STAs including an STA 1 andan STA 2. In response to receiving the RTS frames, the STAs may transmitCTS frames to the AP after an SIFS.

When the CTS frames are received, the AP may transmit the UL MU pollframe to transmission STAs including the STA 1 and the STA 2 after theSIFS. The UL MU poll frame may be transmitted based on MU-MIMOtechnology.

The transmission STAs may transmit data frames including a data frame 1and a data frame 1 after the SIFS from a time at which the UL MU pollframe is received. The data frames may be transmitted based on theMU-MIMO technology.

The AP may receive the data frames, and then transmit ACK framesincluding an ACK1 and an ACK2 to the transmission STAs after the SIFS.The ACK frames may be transmitted based on the MU-MIMO technology. TheACK1 and the ACK2 may include STA1 identification information and STA2identification information, respectively.

The units described herein may be implemented using hardware componentsand software components. For example, the hardware components mayinclude microphones, amplifiers, band-pass filters, audio to digitalconvertors, and processing devices. A processing device may beimplemented using one or more general-purpose or special purposecomputers, such as, for example, a processor, a controller and anarithmetic logic unit, a digital signal processor, a microcomputer, afield programmable array, a programmable logic unit, a microprocessor orany other device capable of responding to and executing instructions ina defined manner. The processing device may run an operating system (OS)and one or more software applications that run on the OS. The processingdevice also may access, store, manipulate, process, and create data inresponse to execution of the software. For purpose of simplicity, thedescription of a processing device is used as singular; however, oneskilled in the art will appreciated that a processing device may includemultiple processing elements and multiple types of processing elements.For example, a processing device may include multiple processors or aprocessor and a controller. In addition, different processingconfigurations are possible, such a parallel processors.

The software may include a computer program, a piece of code, aninstruction, or some combination thereof, for independently orcollectively instructing or configuring the processing device to operateas desired. Software and data may be embodied permanently or temporarilyin any type of machine, component, physical or virtual equipment,computer storage medium or device, or in a propagated signal wavecapable of providing instructions or data to or being interpreted by theprocessing device. The software also may be distributed over networkcoupled computer systems so that the software is stored and executed ina distributed fashion. In particular, the software and data may bestored by one or more computer readable recording mediums.

The methods according to the above-described embodiments may berecorded, stored, or fixed in one or more non-transitorycomputer-readable media that includes program instructions to beimplemented by a computer to cause a processor to execute or perform theprogram instructions. The media may also include, alone or incombination with the program instructions, data files, data structures,and the like. The program instructions recorded on the media may bethose specially designed and constructed, or they may be of the kindwell-known and available to those having skill in the computer softwarearts. Examples of non-transitory computer-readable media includemagnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD ROM discs and DVDs; magneto-optical media suchas optical discs; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory (ROM),random access memory (RAM), flash memory, and the like. Examples ofprogram instructions include both machine code, such as produced by acompiler, and files containing higher level code that may be executed bythe computer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations and methods described above, or vice versa.

Although a few embodiments of the present invention have been shown anddescribed, the present invention is not limited to the describedembodiments. Instead, it would be appreciated by those skilled in theart that changes may be made to these embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined by the claims and their equivalents.

What is claimed is:
 1. A method for transmitting an uplink physicallayer protocol data unit (PPDU) by a station (STA) in a wireless localarea network, the method comprising: receiving, by the STA from anaccess point (AP), a first frame soliciting an immediate response fromone or more STAs including the STA; and transmitting, by the STA to theAP, the uplink PPDU including a second frame, wherein the first frameincludes a plurality of user fields corresponding to the one or moreSTAs, wherein the first frame further includes length information whichis commonly applied to one or more frames, including the second frame,transmitted from the one or more to STAs including the STA, wherein eachof the plurality of user fields includes a partial associationidentifier (AID) of a STA, wherein the uplink PPDU is transmitted aShort Inter-Frame Space (SIFS) after the first frame, and wherein anacknowledgement (ACK) frame is received in response to the uplink PPDUfrom the AP.
 2. The method of claim 1, wherein the length informationindicates a value of a Legacy-Signal (L-SIG) Length field of the uplinkPPDU that is a response to the first frame.
 3. The method of claim 1,wherein the uplink PPDU is transmitted based on a multiple usertransmission scheme.
 4. The method of claim 1, wherein the uplink PPDUincludes one or more data units transmitted by the one or more STAs. 5.The method of claim 1, wherein the ACK frame includes bitmapinformation, and each bit of the bitmap information indicates successfulreception of a data unit of the one or more data units.
 6. The method ofclaim 5, wherein the ACK frame further includes identificationinformation of the one or more STAs.
 7. A method for receiving an uplinkphysical layer protocol data unit (PPDU) by an access point (AP) in awireless local area network, the method comprising: transmitting, by theAP to one or more stations (STAs), a first frame soliciting an immediateresponse from the one or more STAs; and receiving, by the AP from theone or more STAs, one or more second frames in the uplink PPDU, whereinthe first frame includes a plurality of user fields corresponding to theone or more STAs, wherein the first frame further includes lengthinformation which is commonly applied to the one or more second framestransmitted from the one or more STAs, and wherein each of the pluralityof user fields includes a partial association identifier (AID) of a STA,wherein the uplink PPDU is transmitted a Short Inter-Frame Space (SIFS)after the first frame, and wherein an acknowledgement (ACK) frame istransmitted in response to the uplink PPDU to the one or more STAs. 8.An apparatus of a station (STA) for transmitting an uplink physicallayer protocol data unit (PPDU) in a wireless local area network, theapparatus comprising: a transceiver; and a processor, wherein theprocessor is configured to: cause the transceiver to receive, from anaccess point (AP), a first frame soliciting an immediate response fromone or more STAs including the STA; and cause the transceiver totransmit, to the AP, the uplink PPDU including a second frame, whereinthe first frame includes a plurality of user fields corresponding to theone or more STAs, wherein the first frame further includes lengthinformation which is commonly applied to one or more frames, includingthe second frame, transmitted from the one or more STAs including theSTA, and wherein each of the plurality of user fields includes a partialassociation identifier (AID) of a STA, wherein the uplink PPDU istransmitted a Short Inter-Frame Space (SIFS) after the first frame, andwherein an acknowledgement (ACK) frame is received in response to theuplink PPDU from the AP.